The long term objectives of this grant and its Specific Aims are: 1) To elucidate the molecular mechanisms of action of two endogenous inhibitors of angiogenesis previously identified in this laboratory, and 2) To discover other proteins which make up a family of natural angiogenesis inhibitors in the body. The first Aim will focus on the following questions: 1) What is the effect of angiostatin on endothelial cell cycle progression? 2) How does glycosylation effect angiostatin function? 3) How is collagen XVIII processed to endostatin? And 4) What is the molecular mechanism of the specificity of endostatin as an inhibitor of vascular endothelial cells? The second Aim will involve purification and sequencing of a new angiogenesis inhibitor that has recently been detected. They will employ a double tumor model in mice, also called the "concomitant resistance" model. One of these inhibitors is generated by human bladder cancer cells. Endostatin is already in clinical trial. They believe that these inhibitors along with others, yet to be identified and fully characterized, may eventually be added to conventional chemotherapy or to radiotherapy or to immunotherapy to improve efficacy of anti-cancer therapy, to decrease toxicity, and to reduce the development of acquired drug resistance. A study of mechanism of endogenous inhibitors may enlarge their understanding of the family of proteins which operate to suppress angiogenesis under physiological conditions.